Subtropical Storm OTTO (Text)

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SUBTROPICAL STORM OTTO DISCUSSION NUMBER 3
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL172010
500 PM AST WED OCT 06 2010
SATELLITE IMAGERY AND DATA FROM AN AIR FORCE RESERVE RECONNAISSANCE
UNIT AIRCRAFT INDICATE THAT THE SUBTROPICAL DEPRESSION HAS
CONTINUED TO BECOME BETTER ORGANIZED AND HAS STRENGTHEN INTO
SUBTROPICAL STORM OTTO. CONVECTIVE BANDING NOW WRAPS ABOUT 75
PERCENT AROUND THE BROAD INNER CORE WIND FIELD. MAXIMUM 1500-FT
FLIGHT-LEVEL WINDS OBSERVED HAVE BEEN 63 KT IN THE SOUTHWESTERN
QUADRANT...WHICH CORRESPONDS TO ABOUT 50 KT AT THE SURFACE. THIS
VALUE IS CLOSE TO THE 48 KT CREDIBLE SFMR WINDS OBSERVED IN THE
SAME AREA...SO THE INITIAL INTENSITY IS SET AT 50 KT. VISIBLE AND
WATER VAPOR SATELLITE IMAGERY INDICATE THAT A SMALL UPPER-LEVEL
COLD LOW...LOCATED PREVIOUSLY IN THE SOUTHEAST QUADRANT...HAS MOVED
CYCLONICALLY AROUND THE LOW-LEVEL CIRCULATION AND IS NOW SITUATED
ABOUT 30 NMI WEST OF THE LOW-LEVEL CENTER. THIS SUGGESTS THAT OTTO
IS STILL A SUBTROPICAL CYCLONE...BUT THAT IT IS ALSO GRADUALLY
ACQUIRING TROPICAL CHARACTERISTICS.
THE INITIAL MOTION ESTIMATE IS 360/4. THERE ARE NO SIGNIFICANT
CHANGES TO THE PREVIOUS FORECAST TRACK OR REASONING. OTTO IS MOVING
NORTHWARD THROUGH A BROAD WEAKNESS IN A DEEP-LAYER RIDGE WHERE
STEERING CURRENTS ARE WEAK. HOWEVER...A STRONG MID-TROPOSPHERIC
TROUGH LOCATED OVER THE EASTERN U.S. IS FORECAST TO MOVE EASTWARD
AND GRADUALLY NUDGE OTTO ON A NORTHEASTWARD TRACK DURING THE NEXT
24 HOURS...AND THEN RAPIDLY ACCELERATE THE CYCLONE TO THE
EAST-NORTHEAST AHEAD OF A STRONG COLD FRONT BY 36 HOURS. BETWEEN 72
AND 96 HOURS...OTTO IS EXPECTED TO MERGE WITH THE COLD FRONT AND
BECOME A STRONG EXTRATROPICAL LOW PRESSURE SYSTEM THAT MAY POSE A
THREAT TO THE AZORES ISLANDS BY 120 HOURS. THE FORECAST TRACK IS
JUST AN UPDATE OF THE PREVIOUS ADVISORY TRACK AND IS DOWN THE
MIDDLE OF THE TIGHTLY PACKED NHC MODEL GUIDANCE.
OTTO IS EXPECTED TO TRANSITION INTO A TROPICAL CYCLONE WITHIN THE
NEXT 12 HOURS OR SO DUE TO A COMBINATION OF LIGHT VERTICAL WIND
SHEAR...WARM SSTS OF AT LEAST 28C...AND THE EXPECTED DISSIPATION OF
THE SMALL UPPER-LEVEL LOW. THE OFFICIAL INTENSITY FORECAST NOW
CALLS FOR OTTO TO REACH HURRICANE STRENGTH BY 36 HOURS...AND THEN
GRADUALLY WEAKEN AS THE WIND SHEAR INCREASES AHEAD OF THE
AFOREMENTIONED STRONG UPPER-LEVEL TROUGH. BY 96 HOURS...OTTO IS
EXPECTED TO TRANSITION INTO AN EXTRATROPICAL LOW. THE OFFICIAL
INTENSITY FORECAST IS A COMPROMISE OF THE STRONGER SHIPS/LGEM
MODELS AND THE WEAKER GFDL/HWRF MODELS.
FORECAST POSITIONS AND MAX WINDS
INITIAL 06/2100Z 23.2N 68.3W 50 KT
12HR VT 07/0600Z 23.8N 68.5W 55 KT
24HR VT 07/1800Z 24.5N 67.9W 60 KT
36HR VT 08/0600Z 25.5N 66.4W 65 KT
48HR VT 08/1800Z 26.8N 63.7W 65 KT
72HR VT 09/1800Z 30.3N 55.8W 55 KT
96HR VT 10/1800Z 34.5N 44.5W 40 KT...POST-TROP/EXTRATROP
120HR VT 11/1800Z 39.0N 31.0W 35 KT...POST-TROP/EXTRATROP
$$
FORECASTER STEWART
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